This invention relates to a variable contour rubber extruder for continuously extruding rubber having compositions for various uses through a mouth piece into belts and more particularly to a rubber extruder capable of varying cross-section of a mouth piece to obtain particular contours of extruded rubber meeting with various kinds of tires.
A variable mouth piece of a rubber extruder suitable for extruding different tread rubbers for various kinds of tires has been disclosed in, for example, Japanese Laid-open Utility Model Application No. 58-120,022. With this variable mouth piece, sectional curves of its desired contour are approximately designated by polygonal lines to eliminate defects in forming and vulcanizing processes such as creases, bares or light spots or inclusion of air which would occur in prior art stepwise designated curves of mouth pieces. On the other hand, however, the mouth piece designated by polygonal lines encounters a new problem in that contours of extruded rubber would deform at the opening of the mouth piece due to swelling effect uneven in the width direction resulting from a difference in thickness of the contours, so that required contours after water cooling cannot be obtained.